Master mold manufacturing method and mold structure manufacturing method

ABSTRACT

Disclosed is a method of manufacturing a master mold having an uneven pattern which includes wide and narrow concave portions using a reactive ion etching process. The method is capable of manufacturing a master mold improved in the uniformity of concave portions of the uneven pattern by performing a main etching step in which etching is performed, using an original plate which includes a processing target layer and a foundation layer, on the processing target layer using the foundation layer as an etch stop layer and an extra etching step in which etching is performed on the original plate degraded by the main etching step in the uniformity of concave portions in order to improve the uniformity using an etching gas which includes a first gas capable of etching the foundation layer and producing a deposit with a bias power of not greater than 15 W.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a master moldhaving thereon an uneven pattern or a reverse uneven patterncorresponding to a predetermined magnetic pattern or an uneven pattern.The invention also relates to a method of manufacturing a mold structureused for pattern transfer.

2. Description of the Related Art

Technologies for efficiently transferring two-dimensional andthree-dimensional patterns to transfer receiving media (also called as“slave media”), such as a magnetic transfer to a transfer receivingmedium performed in the manufacture of magnetic recording media using amagnetic transfer master disk having thereon a fine magnetic pattern, anano-imprinting on a transfer receiving medium performed in themanufacture of discrete track media (DTM), bit patterned media (BPM),and the like using a nanoimprint mold having thereon a fine unevenpattern, and the like, have been developed as described, for example, inU.S. Patent Application Publication No. 20010028964 and U.S. Pat. No.7,850,441. Such technologies allow the magnetic pattern or unevenpattern to be transferred to a transfer receiving medium at a time bypressing a pattern transfer mold structure (the magnetic transfer masterdisk or nanoimprint mold) onto a transfer receiving medium, whereby finepatterns or fine uneven patterns in the range of nanometers may beformed easily with low costs.

The mold structure needs to have a high uniformity in convex portions ofthe uneven pattern (high flatness in the upper surface of each convexportion and high uniformity in the height of each convex portion) due toits characteristics. For example, if a magnetic transfer master disk hasa low uniformity in convex portions, some of the convex portions are notappropriately brought into contact with a transfer receiving medium whenthe mold is pressed onto the transfer receiving medium, thereby causinga problem that the magnetic pattern is not transferred correctly. In themean time, if, for example, a nanoimprint mold has a low uniformity inconvex portions, pressing of the mold onto a transfer receiving mediumwill result in non-uniform thickness of residual layers (resist filmsnot being completely impressed out and remaining after the imprinting)formed at the bottoms of concave portions of the resist layer of thetransfer receiving medium. In this case, the residual layers aretypically removed through dry etching by setting the etching device suchthat a thickest film is removed. Here, a portion of the foundation layerwith a thin residual layer may be etched or the size (e.g., line widthof a line and space pattern) of the resist pattern with a thin residuallayer becomes smaller that the size of the resist pattern with a thickresidual layer, thereby causing a problem of a varied pattern size.

In the mean time, such mold structure is worn out through repeated use,so that it is normally replicated by electroforming using an originalmold (master mold) having an uneven pattern reverse to the unevenpattern of the mold structure in consideration of the manufacturingefficiency, durability, and cost. In such a case, in order to improvethe uniformity of convex portions of the mold structure, it is necessaryto improve the uniformity of concave portions of the uneven pattern ofthe master mold (high flatness in the bottom surface of each concaveportion and high uniformity in the depth of each concave portion).

As for a specific method of achieving this improvement, Japanese PatentNo. 4189600 teaches a method of manufacturing a master mold through areactive ion etching process in which an original plate constituted by aprocessing target layer (e.g., SiO₂) and a foundation layer (e.g., Si)is used and the foundation layer is caused to act as an etch stop layerby increasing the etching selectivity of the processing target layer,thereby aligning the depth of each concave portion at the interfacebetween the processing target layer and the foundation layer.

The method described in Japanese Patent No. 4189600 is a useful methodof manufacturing conventional media, but the method may cause a problemthat it is difficult to maintain a high uniformity in concave portionsof a master mold in the recent manufacture of media which requirestransfer technology for transferring a fine pattern in the range ofseveral tens of nanometers. In particular, this tendency becomessignificant for a pattern having coarse and fine portions, that is, apattern in which uneven patterns that include a concave portion having arelatively wide space (wide concave portion) and a concave portionhaving a relatively narrow space (narrow concave portion) are arrangedcomplicatedly, such as a servo pattern of a magnetic recording medium.More specifically, although in the method described in Japanese PatentNo. 4189600, the foundation layer is caused to function as an etch stoplayer, the etching can not be stopped completely at the surface of thefoundation layer and the layer is etched by several nanometers. This maycause a problem for an uneven pattern that includes a wide concaveportion and a narrow concave portion that the bottom of the wide concaveportion is etched in an upward convex shape (convex shape) and thenarrow concave portion is etched deeper than the wide concave portion.

The detailed mechanism of the occurrence of this problem is unclear, butthis may be due to formation of “micro trench” in which bottom portionsabutting to side walls are etched deeper than the other portion whenreactive ion etching is performed. That is, it is believed that, for awide concave portion, micro trenches are formed in bottom portionsabutting to side walls and the bottom is shaped in a convex shape and,for a narrow concave portion, micro trenches are merged and the depthbecomes deeper as a consequence. Further, where reactive ion etching isperformed on a nonconductor, such as SiO₂, micro trenches are formedmore significantly due to charging.

The present invention has been developed in view of the circumstancesdescribed above, and it is an object of the present invention toprovide, in master mold manufacturing using a reactive ion etchingprocess, a master mold manufacturing method capable of manufacturing amaster mold having a high uniformity in concave portions of an unevenpattern that includes a wide concave portion and a narrow concaveportion.

It is a further object of the present invention to provide, in moldstructure manufacturing through replication by electroforming with themaster mold manufactured by the master mold manufacturing methoddescribed above as the original master, a mold structure manufacturingmethod capable of manufacturing a mold structure having a highuniformity in convex portions of an uneven pattern that includes a wideconcave portion and a narrow concave portion.

SUMMARY OF THE INVENTION

In order to solve the problem described above, a master moldmanufacturing method of the present invention is a method using anoriginal plate which includes a processing target layer and a foundationlayer in which a coating layer having an opening pattern constituted bya plurality of openings is formed on the processing target layer and anetching step is performed with a reactive ion etching process using thecoating layer as a mask to manufacture a master mold having thereon anuneven pattern corresponding to the opening pattern, wherein:

the opening pattern includes a wide opening having a wide width and anarrow opening having a width narrower than the width of the wideopening; and

the etching step includes:

-   -   a main etching step in which etching is performed on the        processing target layer using the foundation layer as an etch        stop layer; and    -   an extra etching step in which etching is performed on the        original plate, in which a wide bottom surface of a wide concave        portion corresponding to the wide opening has been shaped in an        upward convex and a narrow concave portion corresponding to the        narrow opening has been etched to a depth deeper than a depth of        the wide concave portion by the main etching step, such that the        wide bottom surface is flattened out and the depth of the wide        concave portion corresponds to the depth of the narrow concave        portion using an etching gas which includes a first gas capable        of etching the foundation layer and producing a deposit with a        bias power of not greater than 15 W.

The term “processing target layer” as used herein refers to a primaryetching target layer when forming the uneven pattern of the master mold.Here, the term “primary etching target layer” as used herein refers tothat the layer is etched such that concave portions of the unevenpattern has a depth roughly corresponding to the layer thickness of thelayer.

The term “foundation layer” as used herein refers to a layer having acomposition different from that of the processing target layer and usedas an etch stop layer in the main etching step.

The term “an uneven pattern corresponding to the opening pattern” asused herein refers to an uneven pattern in which a portion of theprocessing target layer not covered by the coating layer is etched andformed into a concave.

The term “wide opening” as used herein refers to an opening having arelative wide width (space width contacting the processing target layer)and the term “narrow opening” as used herein refers to an opening havinga width narrower than that of the wide opening.

The term “wide concave portion” as used herein refers to an area etchedaccording to a wide opening and the term “narrow concave portion” asused herein refers to an area etched according to a narrow opening.

The term “wide bottom surface” as used herein refers to the bottomsurface of a wide concave portion and the term “narrow bottom surface”as used herein refers to the bottom surface of a narrow concave portion.

The term “shaped in an upward convex” as used herein with respect to awide bottom surface refers to that a bottom portion other than theportions abutting to side walls have a raised shape due to that theportions abutting to side walls are etched further than the otherportion, that is, refers to the state in which fine trenches are formedat the portions abutting to side walls.

The term “depth” of a wide concave portion as used herein refers to anaverage distance from the surface of the processing target layer withrespect to a wide concave portion opposite the foundation layer to acentral portion of the wide bottom surface, and the term “depth” of anarrow concave portion as used herein refers to an average distance fromthe surface of the processing target layer with respect to a narrowconcave portion opposite the foundation layer to a central portion ofthe narrow bottom surface.

The term “flat” as used herein with respect to a wide bottom surfacerefers to that difference in depth between a portion of the bottomsurface abutting to a side wall (deepest portion) and a central portionof the bottom surface (shallowest portion) is small.

The term “the depth of the wide concave portion corresponds to the depthof the narrow concave portion” as used herein refers to that thedifference in depth between these concave portions is small.

In the master mold manufacturing method of the present invention, it ispreferable that the etching gas further includes a second gas having agreater capability to etch the foundation layer than the capability ofthe first gas and producing no deposit.

Further, it is preferable that the extra etching step is performed undera pressure of 1 to 12 Pa.

Still further, it is preferable that the extra etching step is performedusing a diluent gas, as well as the etching gas, with an antenna powerof 20 to 200 W.

Preferably, the reactive ion etching process is an etching process whichuses an inductively coupled plasma generation method, a capacitivelycoupled plasma generation method, or an electron cyclotron resonanceplasma generation method, and is capable of independently controllingthe bias power and the antenna power.

Preferably, the reactive ion etching process is an etching process whichuses the inductively coupled plasma generation method;

the processing target layer consists primarily of SiO₂ and thefoundation layer consists primarily of Si; and

-   -   the extra etching step is performed under a flow ratio of 1:1 to        15:1 between the first gas and the second gas and a flow ratio        of 1:1 to 1:20 between the etching gas and the diluent gas.

The term “primarily consisting of” SiO₂ or Si as used herein refers tothat the content of SiO₂ or Si in each layer is 90% by mass or more.

Further, it is preferable that the extra etching step is performed undera flow ratio of 3:1 to 8:1 between the first gas and the second gas, aflow ratio of 1:5 to 1:15 between the etching gas and the diluent gas, apressure of 4 to 8 Pa, and an antenna power of 30 to 100 W.

Preferably, the first gas is at least one type of gas selected from thegroup consisting of CF4, CH2F2, CH3F, C4F8, C4F6, and C5F8, and thesecond gas is SF6.

Preferably, the first gas is CH3F, the second gas is SF6, and thediluent gas is Ar.

A mold structure manufacturing method of the present invention is amethod, including the steps of:

forming, through electroforming of a metal material, a metal substratemade of the metal material on the uneven pattern of a master moldmanufactured by the master mold manufacturing method described above;and

detaching the metal substrate from the master mold to obtain a moldstructure, which is the metal substrate, having an uneven patternreverse to the uneven pattern of the master mold.

In the method of manufacturing a master mold having thereon an unevenpattern corresponding to an opening pattern of coating layer byperforming an etching step with a reactive ion etching process, themaster mold manufacturing method of the present invention includes twoseparate etching steps, a main etching step and an extra etching step,and, in particular, etching is performed in the extra etching step usingan etching gas that includes a first gas capable of etching thefoundation layer and producing a deposit with a bias power of notgreater than 15 W. For an original plate in which a wide bottom surfaceis shaped in an upward convex and a narrow concave portion is etcheddeeper than a wide concave portion by the main etching step, this allowsthe wide bottom surface to be flattened out, and the depth of the wideconcave portion and the depth of the narrow concave portion to beequalized. This advantageous effect is obtained by employing an etchinggas which includes a first gas capable of etching the foundation layerand producing a deposit to make use of the phenomenon that the depositis more likely to be accumulated at a bottom portion abutting to a sidewall, thereby causing a wide bottom portion other than a wide bottomportions abutting to side walls to be etched more than the wide bottomportions abutting to side walls and limiting the bias power to 15 W orless to cause RIE (reactive ion etching) lag (a phenomenon in which awider concave portion is etched deeper). As a result, in the master moldmanufacturing using a reactive ion etching process, a master mold havinghigh uniformity in concave portions of an uneven pattern that includes awide concave portion and a narrow concave portion may be manufactured.

The mold structure manufacturing method of the present inventionincludes the steps of forming, through electroforming of a metalmaterial, a metal substrate made of the metal material on the unevenpattern of a master mold manufactured by the master mold manufacturingmethod described above, and detaching the metal substrate from themaster mold to obtain a mold structure, which is the metal substrate,having an uneven pattern reverse to the uneven pattern of the mastermold. Since the master mold manufactured by the master moldmanufacturing method described above has high uniformity in concaveportions of the uneven pattern, a mold structure having high uniformityin convex portions of an uneven pattern may be manufactured in moldstructure manufacturing in which a mold structure is replicated throughelectroforming using the master mold as the original master.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematic cross-sectional views, illustrating stepsperformed in an embodiment of the master mold manufacturing method ofthe present invention.

FIG. 2 illustrates schematic cross-sectional views, illustrating stepsperformed in an embodiment of the mold structure manufacturing method ofthe present invention.

FIGS. 3A and 3B illustrate schematic cross-sectional views illustratinguneven patterns of an original plate of a master mold before and afteran extra etching process respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings, but the invention is not limitedto these embodiments. Note that each component in the drawings is notnecessarily drawn to scale in order to facilitate visual recognition.

[Master Mold Manufacturing Method]

As illustrated in FIG. 1, a method of manufacturing master mold 10 ofthe present embodiment includes the steps of providing original plate 1having processing target layer 3 and foundation layer 2, forming coatinglayer 4 on processing target layer 3 (A of FIG. 1), forming an openingpattern which includes a wide opening A1 with a width W1 and a narrowopening A2 with a width W2 which is smaller than the width W1 (B of FIG.1), performing main etching on processing target layer 3 by a reactiveion etching process using foundation layer 2 as an etch stop layer andpatterned coating layer 4 as a mask (C of FIG. 1), performing extraetching on original plate 1, in which a wide bottom surface B1 of a wideconcave portion R1 corresponding to the wide opening A1 has been shapedin a convex shape and a narrow concave portion R2 corresponding to thenarrow opening A2 has been etched deeper than the wide concave portionR1 by the main etching, such that the wide bottom surface 51 isflattened out and the depth D1 of the wide concave portion R1corresponds to the depth D2 of the narrow concave portion R2 using anetching gas that includes a first gas capable of etching foundationlayer 2 and producing a deposit, and a second gas having a greatercapability to etch foundation layer 2 than that of the first gas andproducing no deposit, and diluent gas with a bias power of not greaterthan 15 W (D of FIG. 1), and removing remaining coating layer 4 (E ofFIG. 1), thereby manufacturing master mold 10 having an uneven patterncorresponding to the opening pattern.

The method of manufacturing master mold 10 includes four steps, a stepof forming coating layer 4 having an opening pattern, a main etchingstep, an extra etching step, and a step of removing coating layer 4,each of which will now be described in detail.

<Step of Forming Coating Layer Having Opening Pattern>

A of FIG. 1 shows a schematic cross-sectional view, illustrating thestate in which coating layer 4 is formed on original plate 1 which isthe base material of master mold 10. Original plate 1 includes at leastprocessing target layer 3 which is a direct processing target andfoundation layer 2 provided adjacent to processing target layer 3.Formation of original plate 1 in the manner as described above allowsfoundation layer 2 to function as an etch stop layer.

There is not any specific restriction on the material of processingtarget layer 3, and an appropriate material is selected according toetching conditions of etching steps (main etching step and extra etchingstep). Here, a material is selected such that the etching selectivity ofprocessing target layer 2 to coating layer 2 becomes not less than 2,preferably not less than 3, and more preferably not less than 5(indicating that processing target layer 3 is likely to be etched morethan coating layer 2). Generally, the selectivity ratio of not less than2 may ensure a desired etching depth in processing target layer 3 takinginto account the layer thickness of coating layer 4. The selectivityratio can not be determined merely by the type of the material used andit also depends largely on etching conditions. As such, it is preferableto select a material that does not demand a difficult etching condition.In view of ease of film forming and processing, a Si oxide (SiO₂) or aSi nitride (SiN₄) is preferably used as the material of processingtarget layer 3. The thickness of processing target layer 3 serves as arough guide of the depth of a concave portion of an uneven pattern ofmaster mold 10 to be manufactured and, therefore, the thickness isselected appropriately according to a desired depth of the concaveportion, which may be, for example, 20 to 150 nm. There is not anyspecific restriction on the film forming method of processing targetlayer 3, and sputtering, deposition, ion plating, ALD (atomic layerdeposition), CVD (chemical vapor deposition), and the like may be used.Processing target layer 3 may also be formed by oxidizing or nitridingthe surface of a material substrate to be formed into foundation layer2.

There is not any specific restriction on the material of foundationlayer 2. But, it is preferable that the material is selected such thatthe etching selectivity of foundation layer 2 to processing target layer3 becomes ⅕, more preferably 1/10 in the main etching step while itbecomes not less than 5, more preferably not less than 10 in the extraetching step. Selection of the material in the manner as described abovemay prevent the space of a concave portion from being broadened in theextra etching step. In view of the cost and ease of processing, Si ispreferably used as the material of foundation layer 2.

In view of the circumstances with respect to processing target layer 3and foundation layer 2, a Si wafer with a thermal oxide film ispreferably used as original plate 1 which is the base material of mastermold 10.

There is not any specific restriction on the material and film formingmethod of coating layer 4. For example, it may be formed by spin coatingan electron beam resist or the like.

B of FIG. 1 shows a schematic cross-sectional view, illustrating thestate in which an opening pattern is formed in coating layer 4 shown inA of FIG. 1. Coating layer with the opening pattern formed thereinfunctions as a mask in the etching steps. The opening pattern may beprovided, for example, by forming a desired pattern in coating layer 4through electron beam exposure and subsequent development. Preferably,baking is performed to enhance adhesion between original plate 1 andcoating layer 4 after the development. This opening pattern includes awide opening A1 having a wide opening width and a narrow opening A2having a width narrower than that of the wide opening A1. There is notany specific restriction on the value of the opening width, but theproblem that a wide bottom surface B1 is etched in an upward convexshape and a narrow concave portion R2 is etched deeper than a wideconcave portion R1 is more likely to occur when the ratio of an openingwidth W1 of a wide opening A1 to an opening width W2 of a narrow openingA2 is 2 or more. In addition, this problem becomes more significant whenthe opening width W1 of a wide opening A1 is 150 to 200 nm. For example,in a process of manufacturing a master mold required for forming a servopattern of a magnetic recording medium having coarse and fine portions,a coating layer having an opening pattern that includes a wide openingwith a width of 150 to 200 nm and a narrow opening with a width of 75 to100 nm is used as a mask and the aforementioned problem is actuallyhappening.

<Main Etching Step>

In the main etch step, coating layer 4, in which an opening patternhaving a wide opening A1 and a narrow opening A2 is formed, is used as amask and etching is performed on processing target layer 3 from thesurface thereof through openings of the opening pattern by a reactiveion etching process with foundation layer as an etch stop layer.Preferably, an amount of over etching is roughly 10% of the depth of aconcave portion (either a wide concave portion or a narrow concaveportion and, for example, a wide concave portion is used herein).

Preferably, the reactive ion etching (RIE) is an etching process havinghigh perpendicular anisotropy (ion movement tends to occur in the depthdirection of a concave portion) in order to prevent undercut (sideetching), and an inductively coupled plasma (ICP)-RIE, a capacitivelycoupled plasma (CCP)-RIE, or an electron cyclotron resonance (ECR)-RIEis particularly preferable. Further, it is preferable, in the presentinvention, that the bias power (power for forming a bias between theplasma and lower electrode) is controlled independent of the antennapower (power for forming plasma) in order to facilitate control thereof.

The etching condition is set such that etching selectivity of foundationlayer 2 to processing target layer 3 becomes ⅕, preferably 1/10 in orderto cause foundation layer 2 to act as an etch stop layer as describedabove. For example, when the major component of processing target layer3 is SiO₂ and the major component of foundation layer 2 is Si, etchingis performed by the ICP-RIE using CHF3 and CF4 as the etching gas underthe pressure of 0.4 to 10.0 Pa with an antenna power of 50 to 500 W, abias power of 10 to 150 W, and a lower electrode temperature of 60° C.

As coating layer 4 having an opening pattern that includes a wideopening A1 and a narrow opening A2 is used as a mask in the main etchingstep, a wide concave portion R1 and a narrow concave portion R2corresponding to these openings are formed in original plate 1. At thattime, as shown in C of FIG. 1, a phenomenon in which the wide bottomsurface B1 of a wide convex portion R1 becomes upward convex shape and anarrow concave portion R2 is etched deeper than a wide concave portionR1 may occur. This is presumably due to “micro trench” formation inwhich bottom portions abutting to side walls are etched deeper than theother portion when reactive ion etching is performed. It is reportedthat such a micro trench T occurs as a result of increase in ion fluxincident on a portion of a bottom surface abutting to a side wall due toion scattering by a side wall of a convex portion and stimulated etchingof foundation layer 2 by the ion assisted reaction.

As a method for preventing the formation of a micro trench T, it isconceivable, for example, to increase the pressure. This is because ahigh pressure may reduce the ion perpendicular anisotropy and activelycause ion scattering on a side wall, thereby preventing increase in ionflux incident only on a portion of a bottom surface abutting to the sidewall. In this case, however, another problem of increase in edgeroughness of the electron beam resist or non-progress of etching anyfurther (self etch-stop) may possibly occur.

In the mean time, it seems theoretically possible to solve theaforementioned problem by performing etching under a condition in whichthe etching selectivity of the processing target layer is furtherincreased such that the foundation layer is not almost etched.Unfortunately, however, such condition has not been found so far informing a fine uneven pattern, and the etching selectivity is up toabout 10. Further, even if the selectivity ration were furtherincreased, another problem of self etch-stop may possibly occur and,therefore, it is difficult to essentially solve the problem of improvingthe uniformity of concave portions by increasing the etchingselectivity.

<Extra Etching Step>

Consequently, the present invention includes a step of furtherperforming etching (extra etching) on original plate 1 in which a widebottom surface B1 of a wide concave portion R1 is shaped in a convexshape and a narrow concave portion R2 is etched deeper than the wideconcave portion R1 such that the wide bottom surface B1 is flatten outand a depth D1 of the wide concave portion R1 corresponds to a depth D2of the narrow concave portion R2. That is, the present invention haschanged the conventional concept of how to stop etching at the surfaceof foundation layer 2 acting as an etch stop layer and includes a stepof further etching foundation layer 2 (bottom surface of concaveportion) to reshape concave portions of original plate 1 shown in C ofFIG. 1, thereby improving the uniformity of concave portions of mastermold 10 as shown in D of FIG. 1.

The term “flat” as used herein with respect to a wide bottom surfacerefers to that the difference in depth between a portion of the bottomsurface abutting to a side wall (deepest portion) and a central portionof the bottom surface (shallowest portion) is small. Here, thedifference in depth with respect to a wide concave portion is obtainedby extracting, for example, 5 wide concave portions as samples,calculating the depths of the bottom surface portion abutting to a sidewall and the central bottom surface portion of each extracted wideconcave portion through shape measurement by an atomic force microscope(AFM) to obtain a difference between the depths, and averaging thedifferences. A specific value of the difference in depth with respect toa wide concave portion depends on a precision required of a master moldto be manufactured, but a difference in depth of 0.2 nm or less maysometimes be required in the manufacture of media, such as DTM, BPM, andthe like, which requires pattern transfer technology for transferring afine pattern in the range of several tens of nanometers.

The term “depth” of a wide concave portion as used herein refers to anaverage distance from the surface of the processing target layeropposite the foundation layer to the central portion of the wide bottomsurface, and the term “depth” of a narrow concave portion as used hereinrefers to an average distance from the surface of the processing targetlayer opposite the foundation layer to the central portion of the narrowconcave portion. Further, the term “the depth of a wide concave portioncorresponds to the depth of a narrow concave portion” as used hereinrefers to that the difference in depth between these concave portions issmall. Here, the depths of the wide concave portion and narrow concaveportion are obtained through shape measurement by the AFM. A specificvalue of the difference in depth between these concave portions dependson a precision required of a master mold to be manufactured, but adifference in depth of 0.3 nm or less may sometimes be required in themanufacture of media, such as DTM, BPM, and the like, which requirespattern transfer technology for transferring a fine pattern in the rangeof several tens of nanometers.

The present inventor has taken the note that at least the following twofunctions are necessary in the extra etching step in order to realizeetching conditions (type of etching gas and flow rate, use or non-use ofdiluent gas and pressure during etching, antenna power, bias power,lower electrode temperature, and the like) in which the wide bottomsurface B1 is flattened and the depth D1 of a wide concave portion R1corresponds to the depth D2 of a narrow concave portion R2.

(Function 1): A portion of wide bottom surface B1 other than portionsabutting to side walls is etched more than the portions abutting to sidewails.(Function 2): A wide concave portion R1 is etched more than a narrowconcave portion R2.

As a result of deep consideration of the two required functionsdescribed above, the present invention performs extra etching using afirst gas, as the etching gas, capable of etching foundation layer 2 andproducing a deposit in order to obtain the aforementioned function 1.This makes use of the fact that the deposit produced during etching ismore likely to be accumulated at a bottom portion abutting to a sidewall, whereby function 1 may be obtained. The reason why the deposit ismore likely to be deposited at a bottom portion abutting to a side wallmay be presumed that the equilibrium vapor pressure is low at the bottomportion abutting to a side wall in comparison with the other bottomportion and when focusing on a certain product and/or a bi-productproduced during etching, there are more solid surfaces on which theseproduct and bi-product are attached adjacent to the bottom portionabutting to a side wall.

In order to obtain function 2 described above, the present inventionperforms the extra etching with a bias power of 15 W or less. Incomparison with a several hundreds of watts used as the bias power inGeneral RIE, the bias power of the present invention is set to a lowvalue. The low bias power reduces the ion perpendicular anisotropy andions become less likely to go into a narrow concave portion R2(geometrical shadowing effects) and inhibits etching by the ion assistedreaction, thereby causing a RIE lag and providing function 2. The biaspower is preferable to be not greater than 10 W, and particularlypreferable to be 0 W in order to minimize the ion perpendicularanisotropy and to promote RIE lag.

Preferably, the amount of etching in the extra etching step, as a guide,is such that a wide bottom surface B1 is etched about 2 nm under etchingconditions in which the etching selectivity of foundation layer 2 toprocessing target layer 3 becomes not less than 5, and preferably notless than 10 as described above. If the amount of etching in the extraetching step exceeds 10% of a depth D1 of a wide concave portion R1, acentral portion of the wide bottom surface B1 is likely to be etched toomuch. Since a desired depth of concave portions has already been ensuredby the main etching, it is preferable that the amount of etching in theextra etching step is set to a value only necessary for fine adjustmentin depth between a wide concave portion R1 and a narrow concave portionR2.

As for the material of the first gas, fluorocarbon gases which are morelikely to produce a deposit can be used, and CF4, CH2F2, CH3F, C4F8,C4F6, and C5F8 are preferably used, among of which CH3F which producesan appropriate amount of deposit is particularly preferable from theviewpoint of controllability of etching conditions. Use of a gas thatproduces an excessive amount of deposit may lead to degraded etchingcontrollability.

While foundation layer 2 may be etched only with the first gas, it ispreferable that the function of producing a deposit and the function ofetching foundation layer 2 are assumed by different gases from theviewpoint of controllability of etching conditions. Accordingly, it ispreferable, in the present invention, that a second gas having a greatercapability of etching foundation layer 2 than that of the first gas andproducing no deposit is mixed and used as the etching gas other than thefirst gas. As for the material of the second gas, sulfur fluoride gasesmay be used and SF6 is preferably used.

It is further preferable to use a diluent gas (inert gas) with theetching gas. Use of the diluent gas will lead to improvedcontrollability of etching conditions.

It is preferable that the pressure is set to a higher value than apressure (less than 1 Pa) in general etching conditions. A high pressuremay reduce the ion perpendicular anisotropy and cause a more amount ofRIE lag.

As for the antenna power, it is preferable to use a low power in orderto control the etching rate and improve controllability.

Specific values of etching conditions, including the flow rates ofetching gas (first gas and second gas) and diluent gas, pressure,antenna power, and lower electrode temperature, can be set appropriatelyaccording to the etching target of original plate 1. For example, if themajor component of processing target layer 3 is SiO₂ and the majorcomponent of foundation layer 2 is Si, preferable etching conditions forcarrying out the extra etching of the present invention include a flowratio of 1:1 to 15:1 between the first and second gases, a flow ratio of1:1 to 1:20 between the etching and diluent gases, a pressure of 1 to 12Pa, an antenna power of 20 to 200 W, and a bias power of 0 to 15 W. Inthis case, further preferable etching conditions include a flow ratio of3:1 to 8:1 between the first and second gases, a flow ratio of 1:5 to1:15 between the etching and diluent gases, a pressure of 4 to 8 Pa, anantenna power of 30 to 100 W, a bias power of 0 to 15 W, and a lowerelectrode temperature of 10 to 60° C.

There may be a concern that a side wall of a concave portion (processingtarget layer 3) is etched unnecessarily by the extra etching, and thewidth of the concave portion, side wall angle, and the like may possiblybe changed. But, in the present invention, the bias power is set to lowto reduce the kinetic energy given to ions, whereby etching of a sidewall of a concave portion is prevented and virtually no variations inthe width of a concave portion and side wall angle are observed. Morespecifically, when the extra etching is performed such that a widebottom surface B1 is etched by 2 nm under etching conditions in whichthe etching selectivity of foundation layer 2 to processing target layer3 becomes 10 or more, the etched amount of a side wall is about 0.2 nm.

<Step of Removing Coating Layer>

A desired master mold 10 improved in the uniformity of concave portionsas shown in E of FIG. 1 may be obtained by removing coating layer 4 fromoriginal plate 1 improved in the uniformity of concave portions by theextra etching. There is not any specific restriction on the method ofremoving coating layer 4, and removing through ashing may be used as adry process and removing through the use of a peeling solution may beused as a wet process. Note that deposits remaining in concave portionsof the uneven pattern after the extra etching are also removed with thecoating layer by this step.

As described above, in the method of manufacturing master mold 10 havingthereon an uneven pattern corresponding to an opening pattern of coatinglayer 4 by performing etching step with a reactive ion etching process,the method of manufacturing master mold 10 according to the presentembodiment includes two separate etching steps, a main etching step andan extra etching step, and, in particular, etching is performed in theextra etching step using an etching gas that includes a first gascapable of etching foundation layer 2 and producing a deposit with abias power of not greater than 15 W. For negative 1 in which a widebottom surface B1 is shaped in an upward convex and a narrow concaveportion R2 is etched deeper than a wide concave portion R1 by the mainetching, this allows the wide bottom surface B1 to be flattened out andthe depth D1 of the wide concave portion R1 and the depth D2 of thenarrow concave portion R2 to be equalized. As the result, in the methodof manufacturing master mold 10 using a reactive ion etching process,master mold 10 having an uneven pattern constituted by a wide concaveportion R1 and a narrow concave portion and improved in the uniformityof concave portions of the pattern may be manufactured.

(Design Changes of Master Mold Manufacturing Method)

The master mold manufacturing method of the present invention has beendescribed as a method having four steps, but the other step, such as thestep of forming a magnetic layer, step of performing surface treatment,or the like, may also be included as appropriate.

[Mold Structure Manufacturing Method]

A method of manufacturing mold structure 20 of the present invention isa method of manufacturing a mold structure, through replication, byelectroforming using master mold 10 manufactured by the master moldmanufacturing method as the original master and according to the stepsshown in FIG. 2.

More specifically, the method includes the steps of forming conductivelayer 5 along the surface of an uneven pattern of master mold 10 used asthe original master (A of FIG. 2), forming, through electroforming of ametal material using conductive layer 5 formed on the master mold 10 asthe cathode, a metal substrate 6 made of the metal material onconductive layer 5 (B of FIG. 2), and detaching metal substrate 6 frommaster mold 10 (C of FIG. 2), thereby obtaining mold structure 20, i.e.,metal substrate 6, having a reverse uneven pattern to the uneven patternof master mold 10.

The electroforming is performed by immersing master mold 10 in anelectrolyte of electroforming equipment which includes the metalmaterial described above and applying electricity between conductivelayer 5, used as the cathode, and the anode. Here, it is necessary toprovide optimum conditions so that metal substrate 6 (mold structure)produced has no deformation by adjusting the concentration of thematerial in the electrolyte, pH of the electrolyte, way of applyingelectric current, and the like. As for the metal material, Ni ispreferably used from the viewpoint of ease of detachment and durabilitywhen formed into a mold structure.

As for the material of conductive layer 5, metals, such as Ni, may beused and a plurality of conductive layers 5 may be formed on top of eachother. There is not any specific restriction on the method of formingconductive layer and sputtering, deposition, ion plating, ALD (atomiclayer deposition), CVD (chemical vapor deposition), electroless plating,and the like may be used. There is not any specific restriction on thelayer thickness of conductive layer 5 and it is generally a several tensof nanometers. Note that a conductive layer is not necessarily requiredwhen master mold 10 alone has sufficient conductivity forelectroforming, such as the case in which master mold 10 includes ametal layer in its structure.

As described above, the method of manufacturing mold structure 20according to the present embodiment includes the steps of forming,through electroforming of a metal material, metal substrate 6 made ofthe metal material on the surface of the uneven pattern of master mold10 manufactured by the master mold manufacturing method described aboveand detaching metal substrate 6 from master mold 10, thereby obtainingmold structure 20, i.e., metal substrate 6, having a reverse unevenpattern to the uneven pattern of master mold 10. Master mold 10manufactured by the master mold manufacturing method described above hasa high uniformity in convex portions of the uneven pattern.Consequently, mold structure 20 having a high uniformity in convexportions of the uneven pattern may be manufactured in the manufacture ofmold structure 20 through replication by electroforming using mastermold 10 as the original master.

Example

An example of the master mold manufacturing method of the presentinvention will now be described.

<Manufacture of Master Mold>

An original plate having a 60 nm SiO₂ layer (processing target layer)and a 750 μm Si layer (foundation layer) were provided and an 80 nmresist layer was formed on the SiO₂ layer of the original plate. An L&Stype opening pattern having a wide opening with an opening width of 150nm and a narrow opening with an opening width of 75 nm was formed in theresist by electron beam exposure of the resist with an electron beamwriting apparatus and subsequent development.

Thereafter, etching was performed, as the main etching, on the originalplate with an ICP-RIE system (E620, available from Panasonic SolutionsCompany) using the resist layer having the opening pattern formedtherein as the mask under etching conditions for achieving an etchingselectivity of about 10 for the SiO₂ layer with respect to the Si layerin which CHF3 with a flow rate of 30 sccm and CF4 with a flow rate of 15sccm were used as the etching gas with a pressure of 0.6 Pa, an antennapower of 190 W, a bias power of 30 W, and a lower electrode temperatureof 10° C. The amount of over etching was set to 10% (6 nm) of the layerthickness of the SiO₂ layer as a guide.

After the main etching, etching was performed, as the extra etching, onthe original plate with the same ICP-RIE system using the resist havingthe opening pattern formed therein as the mask under etching conditionsfor achieving an etching selectivity of about 12 for the Si layer withrespect to the SiO₂ layer in which CHF3 with a flow rate of 10 sccm andSF6 with a flow rate of 2 sccm were used as the etching gas with apressure of 6.0 Pa, an antenna power of 50 W, a bias power of 0 W, and alower electrode temperature of 10° C. The amount of extra etching in theextra etching step was set such that a wide bottom surface was etched by2 nm.

EVALUATIONS

FIG. 3A illustrates a state of the uneven pattern of the master moldbefore the extra etching step and FIG. 3B illustrates a state of theuneven pattern of the master mold after the extra etching step. The dataof FIGS. 3A and 3B showed that the difference in depth with respect to awide concave portion was about 1.5 nm and the difference in depthbetween a wide concave portion and a narrow concave portion was about 2nm for the master mold before the extra etching step, while thedifference in depth with respect to a wide concave portion was about 0.1nm and the difference in depth between a wide concave portion and anarrow concave portion was about 0.2 nm for the master mold after theextra etching step. This has demonstrated that the uniformity of concaveportions of the master mold is improved by performing the extra etching.

1. A master mold manufacturing method using an original plate whichincludes a processing target layer and a foundation layer in which acoating layer having an opening pattern constituted by a plurality ofopenings is formed on the processing target layer and an etching step isperformed with a reactive ion etching process using the coating layer asa mask to manufacture a master mold having thereon an uneven patterncorresponding to the opening pattern, wherein: the opening patterncomprises a wide opening having a wide width and a narrow opening havinga width narrower than the width of the wide opening; and the etchingstep comprises: a main etching step in which etching is performed on theprocessing target layer using the foundation layer as an etch stoplayer; and an extra etching step in which etching is performed on theoriginal plate, in which a wide bottom surface of a wide concave portioncorresponding to the wide opening has been shaped in an upward convexand a narrow concave portion corresponding to the narrow opening hasbeen etched to a depth deeper than a depth of the wide concave portionby the main etching step, such that the wide bottom surface is flattenedout and the depth of the wide concave portion corresponds to the depthof the narrow concave portion using an etching gas which includes afirst gas capable of etching the foundation layer and producing adeposit with a bias power of not greater than 15 W.
 2. The master moldmanufacturing method of claim 1, wherein the etching gas furthercomprises a second gas having a greater capability to etch thefoundation layer than the capability of the first gas and producing nodeposit.
 3. The master mold manufacturing method of claim 2, wherein theextra etching step is performed under a pressure of 1 to 12 Pa.
 4. Themaster mold manufacturing method of claim 3, wherein the extra etchingstep is performed using a diluent gas, as well as the etching gas, withan antenna power of 20 to 200 W.
 5. The master mold manufacturing methodof claim 4, wherein the reactive ion etching process is an etchingprocess which uses an inductively coupled plasma generation method, acapacitively coupled plasma generation method, or an electron cyclotronresonance plasma generation method, and is capable of independentlycontrolling the bias power and the antenna power.
 6. The master moldmanufacturing method of claim 5, wherein: the reactive ion etchingprocess is an etching process which uses the inductively coupled plasmageneration method; the processing target layer consists primarily ofSiO₂ and the foundation layer consists primarily of Si; and the extraetching step is performed under a flow ratio of 1:1 to 15:1 between thefirst gas and the second gas and a flow ratio of 1:1 to 1:20 between theetching gas and the diluent gas.
 7. The master mold manufacturing methodof claim 6, wherein the extra etching step is performed under a flowratio of 3:1 to 8:1 between the first gas and the second gas, a flowratio of 1:5 to 1:15 between the etching gas and the diluent gas, apressure of 4 to 8 Pa, and an antenna power of 30 to 100 W.
 8. Themaster mold manufacturing method of claim 4, wherein the first gas is atleast one type of gas selected from the group consisting of CF4, CH2F2,CH3F, C4F8, C4F6, and C5F8, and the second gas is SF6.
 9. The mastermold manufacturing method of claim 4, wherein the first gas is CH3F, thesecond gas is SF6, and the diluent gas is Ar.
 10. A mold structuremanufacturing method comprising the steps of: forming, throughelectroforming of a metal material, a metal substrate made of the metalmaterial on the uneven pattern of a master mold manufactured by themaster mold manufacturing method of claim 1; and detaching the metalsubstrate from the master mold to obtain a mold structure, which is themetal substrate, having an uneven pattern reverse to the uneven patternof the master mold.